1. Field of the Invention
This invention relates to a movement detection system for use in detecting movement of a body, such as abnormal movement resulting from failure of a member supporting the body. For example, the system may be used for detecting abnormal movement of a boiler unit in a nuclear reactor, caused by failure of a boiler support.
2. Description of Related Art
In the construction of advanced gas-cooled reactors (AGRs) a number of vertical boiler units are mounted around the reactor core and within the concrete pressure vessel. Heat is extracted from the core by passing carbon dioxide coolant gas over the fuel, and is transferred from the carbon dioxide coolant to the water in each boiler unit. The steam thereby produced drives a turbine to which is coupled a generator.
Each boiler unit is supported on horizontal beams, and these beams are subject to corrosion or erosion by the hot gas which flows around them. Eventually a support beam may fail, resulting in an abnormal movement of the boiler unit.
It is clearly necessary to provide a warning of such failure, and this has previously been effected by a number of different methods. In one such method, mechanical markers have been attached to the boiler units or their supports, so that a visual indication of abnormal boiler unit movement is given. However, such devices can be viewed only by inservice examination equipment during reactor shutdown. In an alternative method, cables which connect reactor temperature monitoring thermocouples to their associated indicators are located in such a manner that they will become severed in the event of abnormal boiler unit movement. This severing will be apparent from the lack of temperature indication. Such a method allows immediate detection of the abnormal movement without waiting for reactor shutdown. However, the method is not wholly reliable, since it is not possible to ensure that any undesirable movement of a boiler unit will necessarily give rise to severing of a cable.